/*
 * Copyright (C) 2012 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.hash;

import com.google.caliper.BeforeExperiment;
import com.google.caliper.Benchmark;
import com.google.caliper.Param;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Random;

/**
 * Benchmarks for comparing {@link MessageDigest}s and {@link com.google.common.hash.HashFunction}s
 * that wrap {@link MessageDigest}s.
 *
 * <p>Parameters for the benchmark are:
 *
 * <ul>
 *   <li>size: The length of the byte array to hash.
 *   <li>algorithm: the algorithm to hash with (e.g. MD5, SHA1, etc.).
 *   <li>hashMethod: how to hash the data (using the Hashing API or the MessageDigest API).
 * </ul>
 *
 * @author Kurt Alfred Kluever
 */
public class MessageDigestAlgorithmBenchmark
{
    @Param({"10", "1000", "100000", "1000000"})
    int size;

    @Param
    Algorithm algorithm;
    @Param
    HashMethod hashMethod;

    private enum HashMethod
    {
        MESSAGE_DIGEST_API()
                {
                    @Override
                    public byte[] hash(Algorithm algorithm, byte[] input)
                    {
                        MessageDigest md = algorithm.getMessageDigest();
                        md.update(input);
                        return md.digest();
                    }
                },
        HASH_FUNCTION_DIRECT()
                {
                    @Override
                    public byte[] hash(Algorithm algorithm, byte[] input)
                    {
                        return algorithm.getHashFunction().hashBytes(input).asBytes();
                    }
                },
        HASH_FUNCTION_VIA_HASHER()
                {
                    @Override
                    public byte[] hash(Algorithm algorithm, byte[] input)
                    {
                        return algorithm.getHashFunction().newHasher().putBytes(input).hash().asBytes();
                    }
                };;

        public abstract byte[] hash(Algorithm algorithm, byte[] input);
    }

    private enum Algorithm
    {
        MD5("MD5", Hashing.md5()),
        SHA_1("SHA-1", Hashing.sha1()),
        SHA_256("SHA-256", Hashing.sha256()),
        SHA_384("SHA-384", Hashing.sha384()),
        SHA_512("SHA-512", Hashing.sha512());

        private final String algorithmName;
        private final HashFunction hashFn;

        Algorithm(String algorithmName, HashFunction hashFn)
        {
            this.algorithmName = algorithmName;
            this.hashFn = hashFn;
        }

        public MessageDigest getMessageDigest()
        {
            try
            {
                return MessageDigest.getInstance(algorithmName);
            }
            catch (NoSuchAlgorithmException e)
            {
                throw new AssertionError(e);
            }
        }

        public HashFunction getHashFunction()
        {
            return hashFn;
        }
    }

    // Use a constant seed for all of the benchmarks to ensure apples to apples comparisons.
    private static final int RANDOM_SEED = new Random().nextInt();

    private byte[] testBytes;

    @BeforeExperiment
    void setUp()
    {
        testBytes = new byte[size];
        new Random(RANDOM_SEED).nextBytes(testBytes);
    }

    @Benchmark
    byte hashing(int reps)
    {
        byte result = 0x01;
        HashMethod hashMethod = this.hashMethod;
        Algorithm algorithm = this.algorithm;
        for (int i = 0; i < reps; i++)
        {
            result ^= hashMethod.hash(algorithm, testBytes)[0];
        }
        return result;
    }
}
